Disk screens are utilized for screening or classifying discrete materials such as wood chips, municipal wastes, and the like. Disk screens are commonly used in the paper industry to separate wood chips on the basis of size prior to pulping. Disk screens have a screening bed with a series of co-rotating spaced parallel shafts, each of which has a longitudinal series of concentric screen disks which interdigitate with the screen disks of the adjacent shafts. Spaces between the disks permit only material of a specified size or smaller size to pass downwardly through the bed of rotating disks. On flat screens, such as U.S. Pat. No. 4,301,930, and split screens, such as U.S. Pat. No. 4,755,286, the disks are driven to rotate in a direction from the infeed end of the screen bed to the outfeed or discharge end of the bed, with the general direction of material flow being perpendicular to the shafts. The particles of material which are larger than the specified size will be advanced on the bed to the outfeed end of the bed and rejected. In so-called V-screens as disclosed in U.S. Pat. No. 4,377,474 the chip flow is generally parallel to the shafts.
Disk screens in which the screen disks are rigidly attached to a central shaft by a method such as welding are susceptible to damage when, in the course of normal usage, foreign objects such as large chips, rock, spurious metal, or other objects enter the screen and lodge between the disks, becoming trapped. If the screen disks are not free to flex so that oversized chips and other foreign objects may be dislodged, breakage or permanent distortion of the disk screen is likely to result.
Disk screens constructed with resilient plastic spacers intermediate between the screen disks, such as the disk screen disclosed in U.S. Pat. No. 4,653,648 alleviate the problems inherent in a rigid disk screen assembly. Prior spacers are usually solid disks of plastic material with portions removed to permit through-bolts for clamping the spacers within the disk screen assembly. Surrounds are known for covering exposed plastic spacers with metal in applications where contamination by plastic is undesirable or where abrasion and deterioration of the plastic may occur prematurely. Use of a metallic surround encircling a resilient spacer is taught in U.S. Pat. No. 4,741,444. Disk screen spacers requiring less plastic material and having a simple geometric shape would advantageously lower costs and conserve resources.